Eds serial switch array

ABSTRACT

In a keyboard, an elastic diaphragm switch array providing mechanical strobe and rollover protection, and/or a serial signal output. The switch includes a diaphragm, a separator, and a switch card. The diaphragm comprises a gold-plated continuous sheet of thin spring material and serves as a ground or voltage plane or voltage adder. The switch card has a conductive switch array (or pie section pattern) at each key location and may have twice as many pie sections as there are bits in the code to be produced or voltage transitions desired in the output, with additional service pie sections as desired. Each pie section is wired directly by double-sided wiring and through-holes in the switch card to the appropriate output code pin, a positive or negative voltage source, or other connection. A key button and distributor is provided for pressing the diaphragm smoothly through the separator to make contact with the corresponding switch card pie section. In each pie pattern, at least one of the pie sections is offset from the center of contact of the key button such that, as the key button is actuated and the diaphragm pressed through the separator, that pie section makes contact at a different point in time to provide a serial code signal output, or provide such service functions as strobe, rollover protection, switch battery power, or the like.

United States Patent Wiedmer [54] EDS SERIAL SWITCH ARRAY [72] inventor: Fritz S. Wiedmer, Saratoga, Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Dec. 21, 1970 [21] Appl.No.: 99,864

[52] U.S. Cl ..200/5 R, 200/16 A, 200/159 B Primary Examiner-Robert K. Schaefer Assistant ExaminerWilliam J. Smith Attorney-Hanifin & Jancin and Shelley M. Beckstrand [451 July 11, 1972 [57] ABSTRACT In a keyboard, an elastic diaphragm switch array providing mechanical strobe and rollover protection, and/or a serial signal output. The switch includes a diaphragm, a separator, and a switch card. The diaphragm comprises a gold-plated continuous sheet of thin spring material and serves as a ground or voltage plane or voltage adder. The switch card has a conductive switch array (or pie section pattern) at each key location and may have twice as many pie sections as there are bits in the code to be produced or voltage transitions desired in the output, with additional service pie sections as desired. Each pie section is wired directly by double-sided wiring and through-holes in the switch card to the appropriate output code pin, a positive or negative voltage source, or other connection. A key button and distributor is provided for pressing the diaphragm smoothly through the separator to make contact with the corresponding switch card pie section. in each pie pattern, at least one of the pie sections is offset from the center of contact of the key button such that, as the key button is actuated and the diaphragm pressed through the separator, that pie section makes contact at a different point in time to provide a serial code signal output, or provide such service functions as strobe, rollover protection, switch battery power, or the like.

10 Chins, 5 Drawing Figures EDS SERIAL swrrcrr ARRAY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrical switching elements for generating an output code, and more particularly to an array of pressure-sensitive elastic diaphragm switching elements which are actuated in a serial fashion and are double-sided wired on a switch card to output pins.

2. Description of the Prior Art This invention is related to the EDS (Elastic Diaphragm Switch) Switch Array and Logic, described in an application of common assignee, Ser. No. 54,300 filed July 13, I970. The description of the prior art contained therein is incorporated herein by reference.

In the prior art devices, as well as in the copending application, Ser. No. 54,300, bufiering logic must be provided to produce a serial output code for data transmission. Also, strobe and rollover protection is provided by the addition of logic circuitry for determining that all contacts have been made, and that there has been no simultaneous depression of keys. This logic circuitry raises the complexity of terminal keyboard, thereby increasing the cost.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved pressure responsive electrical switching element for generating output signals at different times from a single key action.

It is a further object of the invention to provide an improved pressure-responsive diaphragm switch having a plurality of switching elements or pie sections which are double-sided wired on a switch card substrate to output pins for producing a serial output code directly without decoding or encoding log- It is a further object of the invention to provide an improved pressure-responsive diaphragm switch having a plurality of switching elements or pie sections, at least one of which is actuated before or after the others for providing a serial output with a single key actuation.

It is a further object of the invention to provide an improved elastic diaphragm switch having mechanical (as distinguished from electrical logic circuitry),strobe and rollover protection.

The above objects are achieved by the invention which provides an electronic switch means comprising at least one key button, a distributor means, an elastic diaphragm means, separator means, and a switch card means. The switch card comprises a substrate and at least one array of switching elements or pie sections. A plurality of the switching elements or piesections are electrically connected by double-sided wiring on the substrate to the output pin(s) and, in one preferred embodiment, to at least two voltage sources. The elastic diaphragm comprises a thin continuous sheet of conductive and spring material which may be deflected by the key buttons and distributor through the separator into electrical contact with the array of switching elements or pie sections. At least one of the pie sections is offset from the center of contact of the key button by an amount different from that of the ofi'set of the other pie sections (that is, they terminate at diflerent radii). As the key button is actuated, the distributor is compressed and the elastic diaphragm makes contact with the switch card first at the center or on the axis of the key button and then within larger diameters until the key button is actuated to its fully depressed position. Those pie sections which terminate at the smallest radius from the center axis of the key button are first brought into contact with the elastic diaphragm, whereas those pie sections which terminate at the larger radii make contact with the elastic diaphragm at a later point in time.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the switch card array for an eight-key keyboard for generating a serial output code.

FIG. 2 is a cross-section view (not to scale) of the distribu tor, elastic diaphragm, separator, and switch card layers of the serial keyboard of FIG. 1.

FIG. 3 is voltage diagram showing the voltage at the output of FIG. 1 with respect to time as key 100 is actuated.

FIG. 4 is a diagrammatic view of the pie pattern for a key having mechanical strobe and rollover protection.

FIG. 5 is a diagrammatic view of a representative switch array and the associated double-sided wiring for combining two codes and for providing mechanical and electronic strobe.

DESCRIPTION Reference is first made to FIG. 1 of the co-pending application Ser. No. 54,300, showing the elastic diaphragm switch key including button 40, distributor 50, diaphragm 51, separator 52, and switch card or base 60. Reference is made to page 5, line 19, to page 9, line 6, wherein that structure is explained.

Referring again to FIG. 1 of the co-pending application, the expanding diameter of contact between layers 51 and 60 will be described. Therein, as key button is depressed, actuator 46 is driven downwards compressing and deflecting distributor 50 such that conductive layer 51 is brought into contact with surface Y of switch card 60 through the hole U in separator 52. The first point of contact between layers 51 and 60 cc curs immediately beneath and at the axis of actuator 46. As key button 40 continues downward, the distributor 50 drives or forces more of layer 51 into contact with layer 60 in succesv sively larger diameters of contact. The distributor 50 action transforms the actuator motion into the expanding contact area after the first contact due to the fact that as soon as the distributor downward motion is stopped, a horizontal expansion motion occurs in-the elastic material of the distributor.

Inasmuch as distributor 50 is elastic, the material maintains its volume. Thus, as key button 40 is actuated, the distributor first is forced through the separator 52, making contact with card 60, then spreads out in the expanding circle, and returns. The diaphragm and the distributor can be made of one piece, depending upon the elasticity of the material selected.

As will be more fully described, with the various pie sections terminated at different radii about the axis of actuator 46, said pie sections are brought into electrical contact with layer 51 at different points in time according to the diameter of contact between layers 51 and 60.

Referring now to FIG. 1 of this specification, a description will be given of the serial keyboard of the invention. Switch arrays or keys 000, 001, 010, 011, 100, 101, 110, and 111, are deposited gold plated, or other wise provided as conductive patterns on switch card 12. A more detailed representation is given for only key 000, showing that the various pie elements A, B, C, D, E, F, terminate at different radii ab out the center of said key. It should be understood that these reference letters apply to the corresponding pie sections of all the keys. Thus, for each of the keys, the pie section A terminates at the smallest radius and the pie section F terminates at the largest radius with pie sections B-E terminating at increasing radii in a clockwise fashion. Through holes or conductive via-holes J-P are similarly associated with the corresponding pie sections F A for interconnecting said pie patterns and the land patterns on the top of switch card 12 with the land patterns on the bottom of said switch card. In FIGS. 1 and 5, land patterns appearing on the top of card 12 are shown in solid lines while those appearing on the bottom of card 12 are shown in dotted lines.

Each pie section A-F of each key 000-111 is connected by double-sided wiring and via or through-holes to either +12 volts pin 26 or l2 volts pin 27. The elastic diaphragm layer 16 is held in constant contact at 28 with switch card 12. The output pin 36 is connected through resistance 34 to ground voltage 35 and to contact 28.

As will be described in connection with the output of FIG. 3 hereafter, each pair of pie patterns A-B, C-D, and BF, have one of the pair connected to the +12 voltage pin 26 and the other to the -l 2 voltage pin 27, and each pie section A-F for a given switch array is connected to its voltage source through a different resistor 31-33, 41-43.

+12-voltage source at pin 26 is connected through resistance 31 along wire 301 to pie section 000F; thence through via hole 000.1 along line 302 and through via hole 001] to pie section 0011"; thence along line 303 and via hold 010.1 to pie section 010F; thence along line 304 and via 011.1 to pie section 011F; thence along line 305 to pie section 111B; thence through via hole 111K and line 306 through via hole 110K to pie section 11015; thence along line 307 and via hole 101K to pie section 101E; thence along line 308 and through via hole 100K to pie section 100E.

+12-voltage source at 26 is connected along line 30 through resistance 32 and along line 311 to pie section 001D; thence through via hole 001L and land pattern or wire 312 and through via hole 000L to pie section 000D; thence along line 313 to pie section 100D; thence through via hole lL and line 314 and through via 101L to pie section 101D and along line 315 and via 110M to pie section 110C and thence along 316 and via 111M to pie section 111C; and from pie pattern 000D, along line 317 and via 010M to pie section 010C; thence along line 318 and via 01 1M to pie section 011C.

+12-volt source at 26 is connected through resistance 33 7 along line 321 to pie section 010B; thence along via hole 010N and line 328 and via 011P to pie section 011A; from pie section 010B along line 324 to pie section 110B; thence through via hole 110N along line 327 and via hole 1 1 IP to pie section 111A; from pie section 1108, through via hole ll0N along line 325 and via hole 1011 to pie section 101A; thence along line 326 and via hole 1 10N to pie section 100B; also, from pie section 010B through via 010N along 322 and through via hole 001? to pie section 001A; thence along line 323 and through via hole 00N to pie section 00B.

12 volts at 27 is connected through resistance 41 along line 401 to pie section 00B; thence through via hole 000K along line 402 and through via hole 001K to pie section 001E; thence along line 403 and through via hole 010K to pie section 01013; thence along line 404 and through via hole 011K to pie section 011E; thence along line 405 to pie section 111F; thence along through via hole 11 1.1 along line 406 and through via hole 110.1 to pie section 1 10F; thence along 407 and through via hole 101] to pie section 101F; thence along 408 and through via hole 100.1 to pie section 1001 -l 2-volt input at 27 is connected through resistance 42 along line 421 to pie section 001C; thence through via hole 001M along line 424 and through via hole 000M to pie section 000C; thence along line 425 to pie section 100C; thence through via hole 100M along line 426 and through via hole 101M to pie section 101C; thence along line 427 and through via hole 110L to pie section 1 10D; thence along line 428 and through via hole 111L to pie section 111D; from pie 001C through via hole 001M along line 422 and through via hole 010L to pie section 010D; thence along line 423 and through via hole 011L to pie section 011D.

Finally, --1 2-volt input at 27 is connected through resistance 43 along line 430 to pie section 010A; thence through via hole 0101" along line 437 and through via hole 000? to pie section 000A; from pie section 010A through via hole 010? along line 431 and through via hole 011N to pie section 011B; thence along line 433 through via hole 011N along line 436 and through via hole 101N to pie section 10113; from pie section 1118 through via hole lllN along line 434 and through via hole 110! to pie section 110A; thence along line 435 and through via hole 100? to pie section 100A.

The land patterns, lines or wires referred to in FIG. 1 and shown as dotted lines are provided on surface 17 of switch card 12 as shown in FIG. 2, and those which appear in FIG. 1 as solid lines are deposited or otherwise provided on surface 13 of switch card 12 as shown in FIG. 2. The various via holes J-P go through switch card 12 to interconnect surfaces 13 and 17. Elastic diaphragm layer 16 is provided on the bottom surface of distributor 15, as shown in FIG. 2.

Referring now to FIG. 3, the voltage output at pin 36, representing the summation of all voltage drops between pins 26 and 27 to ground 35 through diaphragm plane 16 will be described for key 110. Before the key button actuator corresponding to key position is depressed, the output at pin 36 is represented as 0 voltage 9 in FIG. 3. As the key is depressed, the first pie section to draw current is 011A, that pie section which extends furthest in toward the section of the key switch array or which terminates at the smallest radius. With pie section 110A in contact with diaphragm 16, current flows from negative voltage source 27 through resistance 43 and 34 to ground pin 35, resulting in the negative voltage at output pin 36 is shown as the negative signal at 9A in FIG. 3. As the key button is further depressed, the diameter of the area of contact between diaphragm 16 and switch card 12 increases unu'l pie section 110B makes contact with the diaphragm 16. At that time, the +12 voltage source at pin 26 is connected to ground 35 through resistances 33 and 34. The output voltage which appears at 9B in FIG. 3 is zero, representing the division of the voltage across resistances 33 and 43. As the diaphragm contact circle reaches out to include pie section 1 10C, current is drawn through resistance 32 from the positive voltage source and added to the current being drawn through pie sections 110A and 1108 to produce the positive output voltage 9C at pin 36. As pie section 110D makes contact with the diaphragm 16, current is drawn through resistance 42 from the negative voltage source; when added to the other currents, this gives a zero current through resistor 34 or zero 9D output at pin 36. Finally, as the diaphragm 12 makes contact with the pie sections 110E and 110F, those pie sections which terminate at the largest radii, current is drawn through all resistances 31-33 and 41-43, and added to produce an output 9F of zero at output pin 36. When the key button is released, the reverse process takes place; the circumference of the area of contact of diaphragm 16 with switch card 12 becomes smaller until all contact is lost and a zero output voltage 8 appears at pin 36.

In summary, herein, each pie section A-F of a given key, such as key 110, is connected to either a 12K resistor which is connected to +12 volts or a 12K resistor connected to 12 volts. Each bit position is made out of two consecutive pie shapes, one of which is connected to the positive voltage and the other to the negative voltage. Depending on sequence in which they are connected, a positive or negative current pulse will flow through the diaphragm for each output code bit. The diaphragm 16 is connected to ground 35 over the 1K resistor 34 across which the output voltage is generated. Such a keyboard, therefore, has 2N l resistors where N is the number of bits on the code. The code is produced in reverse when the key is lifted and this can be used for error detection.

While the serial switch array shown in FIG. 1 at switch 000 shows each switch element A-F terminating at a slightly larger radius from element to element in a clockwise direction, it is not necessary that adjacent pie sections terminate on adjacent radii. For the purposes of the serial configuration described in FIGS. 1 and 3, it is only essential that the two pie sections comprising a given bit in the output code terminate on adjacent radii. Thus, for example, while pie section A and 13 must terminate on adjacent radii, they need not be placed adjacent to each other in the pattern shown.

The operator of the keyboard may require some form of feedback to know that he has depressed a given key all the way to make contact between the diaphragm and all of the pie sections. Feedback can be provided by light or by a tone or visually as by TV display change. The feedback can be generated by an additional pie section with greater radius than all others or by electronic logic.

Referring now to FIG. 4, the pie section array for a single key on a keyboard having mechanical strobe and rollover protection will be explained. Starting with a standard six pie sposition 52-57 switch array similar to those described in the copending application, two service pie sections 51 and 58 are added. One service pie section 51 comes further to the center 50 than all the o ers and therefore will make the first or early contact with the diaphragm as it is depressed into contact with the switch card by the key actuator. This pie section 51 may be used to provide rollover protection between keys. That is, each early contact, when made, draws a small current through a resistor (not shown) and these currents are summed in a common resistor. The voltage discriminator to detect whether or not two early pie sections 51 from more than one key are simultaneously depressed. If no rollover protection is necessary, it is still desirable to fill the center of the pie switch with say, gold-plated copper so that there are no holes in the surface presented to the diaphragm that are larger than the separation between the pie sections of approximately 5 mil.

This is done in order to exclude the possibility of permanent deformation of the diaphragm. The data pie sections 52-57 end far enough from the center so that none is contacted before the early contact is made to pie section 51 at portion 50. The other service pie section 58 ends still further out from the center so that it is always made" (or contacted) last, and therefore it can be used to strobe the data pie sections. If rollover is not used, this strobing would be done by supplying data common to the diaphragm through the strobe-pie section.

Referring further to FIG. 4, a battery-operated terminal variation of the embodiment described above will be discussed. In a battery-operated terminal, it is important that the battery be used only during actual key depression and not in between key operation or during idle time of the terminal. In such a terminal, the code would be generated by pie sections 52-57 and either pie section 51 or 58 of all the key positions in the keyboard would be connected in parallel to operate a reed relay, for instance, that connects the battery to the terminal electronics. If current consumption is low enough, the paralleled pie sections 51 or 58 themselves can be used to connect, say, the diaphragm to the battery ground terminal.

Referring now to FIG. 5, a further embodiment of the invention will be described. In FIG. 5, only one key of a plurality of key positions in a keyboard is shown. Pie positions 62, 64, and 66 are shown connected to wires 61, 63, and 65 to a circuit block 60 which includes, for example, the 12 output code of a 3 of 14 code terminal as described in the co-pending application. Circuit 60 may further include electronic strobe and rollover protection as described in said application. Key locations 71-79 are similarly shown connected to circuit box 70 by double-sided wiring including lines 81-89 and 91-93, 98, 99. Circuit 70 represents the output code pins, for example, of an ASCII, BCD, or EBCDIC device. As shown, pie sections 62, 64, 66, terminate at a larger radius than pie sections 71-79. In this manner, it is possible to generate two output codes from a single key switch array, and to combine mechanical and electronic strobe. Thus, the 3 of 14 code generated in circuit 60, for example, may include electronic strobe and rollover. Then, the code generated in circuit 70 may be strobed by the contact of the three short pie sections 62, 64, 66, represented by the electronic strobe on these contacts.

As will be apparent, many possible combinations of short and long pie sections, connected by double-sided wiring to different utilization devices, may provide different output codes and utilize various strobe and rollover protection techniques.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A keyboard switch means for making a plurality of contact closures, comprising a conductive diaphragm,

a plurality of pie sections, with at least two of said sections terminating on different radii,

key and distributor means for moving said conductive diaphragm into contact with said pie sections,

whereby as said key is depressed, at least two of said sections contact said diaphragm at different times.

2. A serial keyboard apparatus comprising elastic diaphragm switch means for making a plurality of contact closures comprising a conductive diaphragm,

a plurality of pie sections, each said section terminating at different radii, with each pair of pie sections terminating on adjacent radii defining a bit in the code,

actuating means for bringing said diaphragm into contact with said pie sections in a serial fashion,

a positive voltage source a negative voltage source,

each said pair having one pie section connected to said positive source and the other pie section to said negative source,

voltage summation means connected to said diaphragm for summing the voltages of all said pie sections in contact with said diaphragm,

whereby as the key is depressed, the diaphragm contacts the pie sections in a serial manner and a summation of the voltages of said sections represents the serial code output of said switch.

3. An elastic diaphragm switch array, comprising a conductive diaphragm,

a plurality of pie sections,

actuating means for moving said diaphragm into contact with said pie sections,

each said pie section terminating at a different radius from the axis of said actuating means.

4. In an elastic diaphragm switch, a plurality of contact closures comprising a conductive diaphragm,

a plurality of pie sections,

actuating means for bringing said diaphragm and pie sections into electrical contact,

at least one of said pie section terminating at a radius different from the radii of termination of the other sections from the axis of said actuating means.

5. An elastic diaphragm switch keyboard for generating at least two output codes, comprising a plurality of switch arrays, each said array comprising at least two groups of pie elements with one group terminating at different radii than the other group, and with said one group connected to output pins associated with one code and said other group connected to output code pins associated with the second code, a conductive diaphragm, and actuating means for bringing said diaphragm and said pie elements into electrical contact.

6. The switch array of claim 5 characterized by means for detecting the closure of those switch arrays included in the group terminating at the largest radii for strobing the output code generated by the group terminating at the smaller radii.

7. In an elastic diaphragm switch keyboard, a switch array comprising a plurality of pie sections, with one pie section extending into the center, and a second pie section terminating at a radius which is greater than the radii at which the remaining pie sections terminate, conductive diaphragm means, and actuating means for bringing said pie sections and said diaphragm into electrical contact whereby mechanical strobe and rollover protection is provided.

8. In an elastic diaphragm switch keyboard having a plurality of switch arrays, each array having a plurality of pie sections, rollover protection means comprising for each said array a control pie section extending to the center axis of the corresponding switch actuator, and means for detecting simultaneous actuation of two said control sections in different switch arrays.

9. In an elecuical diaphragm switch array, mechanical strobe means comprising a conductive diaphragm,

a plurality of pie sections,

actuating means for bringing said diaphragm and pie sections into electrical contact,

' one of said pie sections terminating at a radius larger than the radii about the axis of said actuating means at which the other pie sections terminate.

10. In a battery-operated elastic diaphragm switch keyboard, a switch comprising a conductive diaphragm,

a plurality of pie sections, 

1. A keyboard switch means for making a plurality of contact closures, comprising a conductive diaphragm, a plurality of pie sections, with at least two of said sections terminating on different radii, key and distributor means for moving said conductive diaphragm into contact with said pie sections, whereby as said key is depressed, at least two of said sections contact said diaphragm at different times.
 2. A serial keyboard apparatus comprising elastic diaphragm switch means for making a plurality of contact closures comprising a conductive diaphragm, a plurality of pie sections, each said section terminating at different radii, with each pair of pie sections terminating on adjacent radii defining a bit in the code, actuating means for bringing said diaphragm into contact with said pie sections in a serial fashion, a positive voltage source a negative voltage source, each said pair having one pie section connected to said positive source and the other pie section to said negative source, voltage summation means connected to said diaphragm for summing the voltages of all said pie sections in contact with said diaphragm, whereby as the key is depressed, the diaphragm contacts the pie sections in a serial manner and a summation of the voltages of said sections represents the serial code output of said switch.
 3. An elastic diaphragm switch array, comprising a conductive diaphragm, a plurality of pie sections, actuating means for moving said diaphragm into contact with said pie sections, each said pie section terminating at a different radius from the axis of said actuating means.
 4. In an elastic diaphragm switch, a plurality of contact closures comprising a conductive diaphragm, a plurality of pie sections, actuating means for bringing said diaphragm and pie sections into electrical contact, at least one of said pie section terminating at a radius different from the radii of termination of the other sections from the axis of said actuating means.
 5. An elastic diaphragm switch keyboard for generating at least two output codes, comprising a plurality of switch arrays, each said array comprising at least two groups of pie elements with one group terminating at different radii than the other group, and with said one group connected to output pins associated with one code and said other group connected to output code pins associated with the second code, a conductive diaphragm, and actuating means for bringing said diaphragm and said pie elements into electrical contact.
 6. The switch array of claim 5 characterized by means for detecting the closure of those switch arrays included in the group terminating at the largest radii for strobing the output code generated by the group terminating at the smaller radii.
 7. In an elastic diaphragm switch keyboard, a switch array comprising a plurality of pie sections, with one pie section extending into the center, and a second pie section terminating at a radius which is greater than the radii at which the remaining pie sections terminate, conductive diaphragm means, and actuating means for bringing said pie sections and said diaphragm into electrical contact whereby mechanical strobe and rollover protection is provided.
 8. In an elastic diaphragm switch keyboard having a plurality of switch arrays, each array having a plurality of pie sections, rollover protection means comprising for each said array a control pie section extending to the center axis of the corresponding switch actuator, and means for detecting simultaneous actuation of two said control sections in different switch arrays.
 9. In an electrical diaphragm switch array, mechanical strobe means comprising a conductive diaphragm, a plurality of pie sections, actuating means for bringing said diaphragm and pie sections into electrical contact, one of said pie sections terminating at a radius larger than the radii about the axis of said actuating means at which the other pie sections terminate.
 10. In a battery-operated elastic diaphragm switch keyboard, a switch comprising a conductive diaphragm, a plurality of pie sections, actuating means for bringing said diaphragm and said sections into electrical contact, one of said sections terminating at a different radius from the others and said one section being connected to a battery for drawing current to operate the keyboard only when the switch array is actuated. 